1. Field of the Invention
The present invention relates to a television meeting unit, a television meeting system, and a method for controlling a television meeting system, and particularly relates to a television meeting unit, a television meeting system, and a method for controlling a television meeting system capable of shortening the time required to display a picture of meeting participants to a new participant who participates in the middle of a meeting.
2. Description of Prior Art
Heretofore, a unit for multiplying the picture and voice at multiple points, namely so-called MCU (Multipoint Control Unit), is needed to hold a television meeting between multiple points.
However, with development of the Internet recently, the group broadcast function so-called multicast has been available, and as the result it becomes possible by use of the multicast to hold an electronic meeting between multiple points without preparation of a particular unit such as MCU.
FIG. 1 and FIG. 2 show a typical exemplary structure of a multicast television meeting system that uses the picture and voice. FIG. 1 shows a connection diagram to a network, and FIG. 2 is a functional block diagram for showing a schematic structure of terminal unit. The picture and voice generated from the respective terminal units 12-1 to 12-x are transmitted broadcasterly to the respective terminal units 12-1 to 12x, and the received picture and voice are displayed individually or in the synthesized form to realize the television meeting.
The picture and voice of a television meeting system in the form of compressed code are transmitted usually because of the communication capacity restriction. Typically, H. 261 format or MPEG1 format is used as the picture compression coding system. In these picture compression coding systems, the in-frame coded picture in which the pixel value is coded as it is and the inter-frame prediction coded picture are used with switching selectively. The time redundancy of the picture with slight motion and change is reduced by use of the inter-frame prediction coded picture in which the difference between the previous frame and the next frame is coded because the next frame is very similar to the previous frame. On the other hand, in the case of the picture with quick motion or scene change, the in-frame coded picture is used effectively in which the pixel value is coded as it is used effectively because the correlation between frames is slight. In the general television meeting, the in-frame coded picture is transmitted at first and then the inter-frame coded picture is transmitted thereafter because the motion is not so quick.
At first in the case that a participant terminal participates in the middle in the conventional multicast meeting unit, the new participant receives the inter-frame prediction coded picture that is the meeting data served up to that time. Therefore, the terminal that participates in the middle and receives the inter-frame prediction coded picture cannot display a normal picture because no reference picture (in-frame coded picture) is available, or cannot display the picture until it receives an in-frame coded picture.
At second in the case that the processing capability of the new participant terminal is different, it is required for every participant terminal to perform with a set value within the processable range and furthermore it is required to change the set value due to the middle participation.